1. Field of the Invention
The present invention relates to a pigment-based ink composition containing a polyether-modified polysiloxane, which ink composition can realize good image on plain paper.
2. Background Art
Ink jet recording is a recording method wherein ink is ejected as droplets from fine nozzles to record letters or figures onto the surface of recording media. Various properties are required of inks used in ink jet recording. Examples of properties required of such inks include good dispersion stability, ejection stability, and rubbing/scratch resistance of prints.
Inks comprising various water-soluble dyes dissolved in aqueous media have been generally used. Inks comprising pigments dispersed in aqueous media have also been provided. This pigment-based ink is advantageously superior in waterfastness and lightfastness to a dye-based ink.
Dyes penetrate recording media, such as paper, and are fixed thereto. On the other hand, pigment particles do not basically penetrate recording media, such as paper, and stay thereon and develop color. Therefore, pigment-based ink compositions are likely to be influenced by the surface state of the recording media. The so-called xe2x80x9cplain paperxe2x80x9d causes uneven fixation of pigments due to fuzz of paper fibers and is less likely to realize images having good quality. For this reason, recording media having a smooth and homogeneous surface, that is, the so-called xe2x80x9cspecialty paper,xe2x80x9d are provided, and pigment-based ink compositions are printed on the specialty paper to realize high-quality images.
However, there is still a demand for the realization of high-quality images using pigment-based ink compositions on plain paper which is inexpensive and is widely spread.
On the other hand, modified polysiloxane compounds are known as one of silicone surfactants. Several ink compositions containing this compound are also known. For example, Japanese Patent Laid-Open No. 66470/1984 discloses a lithography ink composition containing an organo-modified polysiloxane. Japanese Patent Laid-Open No. 173068/1985 discloses an ink composition comprising a modified polysiloxane as an antifoaming agent. Japanese Patent Laid-Open Nos. 169790/1993 and 310732/1998 disclose ink compositions for ink jet recording, containing a modified polysiloxane having a specific structure. Further, Japanese Patent Laid-Open No. 279871/1998 discloses a dye-based ink composition comprising a polyether-modified polysiloxane.
The present inventors have now found that an ink composition comprising a polyether-modified polysiloxane having a specific structure can realize good images on plain paper.
Accordingly, it is an object of the present invention to provide an ink composition which can realize good images on plain paper, and, especially when used in an ink jet recording method, can have excellent ejection stability, storage stability, color development, and fixation and is much less likely to cause color bleeding and uneven printing and thus can realize good image quality.
According to one aspect of the present invention, there is provided an ink composition comprising at least a pigment, a compound represented by formula (I), water, and a water-soluble organic solvent: 
wherein
R1 to R7 each independently represent a C1-6 alkyl group,
j and k are each independently an integer of 1 or more,
EO represents an ethyleneoxy group,
PO represents a propyleneoxy group,
m and n are an integer of 0 (zero) or more, provided that m+n is an integer of 1 or more, and
EO and PO may be arranged, regardless of order in the parentheses [ ], randomly or as blocks joined together.